The first known epidemic of drug-resistant typhoid is spreading in Pakistan, raising fears that more diseases worldwide are heading towards being untreatable.

The typhoid superbug, which is resistant to five types of antibiotics, has infected at least 850 people since 2016.

Experts fear it could radiate globally, replacing weaker strains of the disease, The New York Times reported.

There is only one oral antibiotic left that is effective against the strain, but with just one more genetic mutation, doctors would be powerless to fight it, say researchers.

It is the latest sign the world could be heading towards a return to a pre-antibiotic era, following increasing worldwide concern about widespread overuse of the drugs.

Without antibiotics, simple illnesses and common infections would become deadly.

The World Health Organisation has previously described antibiotic resistance as a “global health emergency”.

“This isn’t just about typhoid,” Dr Rumina Hasan, a pathology professor at the Aga Khan University in Pakistan, told the paper. “Antibiotic resistance is a threat to all of modern medicine — and the scary part is we’re out of options.”

Four deaths have been reported so far, according to Pakistan’s National Institute of Health Islamabad. At least one travel-related case has been detected in the UK.

Researchers from Britain’s Wellcome Sanger Institute who analysed the genetics of the new typhoid strain found it had mutated and acquired an extra piece of DNA to become resistant to multiple antibiotics.

Pakistani researchers say poor infrastructure, low vaccination rates and overpopulated city centres all contribute to the spread of typhoid, which is common in the country.

Typhoid is a highly contagious infection contracted by consuming contaminated foods or drinks. Symptoms include nausea, fever, abdominal pain and pink spots on the chest. Untreated, it can be fatal.

About 21m people contract typhoid each year, and about 161,000 die, according to the World Health Organisation.

The only remaining effective drug against the disease is Azithromycin.